1. Field of the Invention
The present invention relates to molded plastic fluid filters, particularly those which have a rigid frame and a sheet material extended between the members of the frame, the sheet material having holes to allow fluid passage while filtering solids out.
2. Description of the Prior Art
Various types of filters are used for removing particles of solid or semi-solid matter which are greater than a selected size from fluids which must be maintained at a certain degree of purity or quality. Small filters commonly used for separating smaller solid particles from fluids are often formed of a rigid frame and screens, formed from another type of material, then are stretched on the rigid frame. The screen in these types of filters usually consist of woven materials. The threads in a woven filter screen can shift to create varying hole sizes, which is not desirable. Generally woven materials for filter screens must also have a seam where the material is joined to itself or overlapped. To join the frame and screen together, most commonly the sheet of screen material is inserted into the mold in which the frame is molded. This makes conventional filters complex to manufacture because of the need for precision placement of the screen material in the mold with the seam properly located so that the molded frame will support it. Other types of filters have been formed from plastic mesh material which is first molded into substantially flat sheets having slots or holes therein, and then are rolled to form a cylinder having a seam where the two ends of the sheet are joined. Such a filter is disclosed in U.S. Pat. No. 4,406,326 to Wagner. The Wagner filter is produced by injection molding a sheet having a large plurality of V-shaped slots, then roll-forming the sheet into a cylindrical shape, and then finally bonding its longitudinal edges together.
One type of filter is known which has been molded by a single step process. U.S. Pat. No. 4,052,315 to Lindsay Jr., et al. discloses a one piece molded fluid filter having a base portion with fluid passageway therethrough, a head portion spaced axially from the base a selected distance, a plurality of axially spaced apart annular rings positioned between the base portion and the head portion, a plurality of arcuately spaced axially disposed ribs extending between the base and head portions and extending solely in a direction radially inward from an internal juncture of the radially outer edges of the ribs so that the ribs and annular rings cooperate to provide a multiplicity of predetermined size filtration openings at the junctures between the ribs and rings. The fluid passageway in the Lindsay filter are formed by the junctures of the annular rings and axially disposed ribs, and not by holes through a screen material. Some of the ribs and rings do form a frame structure in the Lindsay filter, however, the remaining ribs and rings could not be said to form a screen material with holes therethrough.
Engraving equipment, such as a computer controlled orbiting cutter, has been used in the past to create decorative designs and indicia on molds which are used in the manufacture of plastic products. A resist and photo etching process has also been used to engrave decorative designs on these molds.